This invention relates in general to tools for disassembling threaded fasteners and, more specifically, a tool for removing round collars from threaded bolts.
A fastening system for aerospace structures, as detailed in U.S. Pat. Nos. 2,940,495 and 3,138,987 has achieved widespread use in the aerospace industry due to its simplicity, consistently controlled preload and minimum size and weight. The fastener basically consists of two parts, a threaded bolt and threaded nut. The nut, which is the key component, consists of a internally threaded collar which threads onto the bolt and has a bearing surface which engages the structure being fastened and a wrenching device which is unitary with the collar and typically has a hexagonal cross-section for engagement by a conventional wrench. The bolt end has a configured recess, typically hexagonal, so that an Allen wrench may be inserted to hold the bolt stationary while the nut is rotated. A groove is provided between the wrenching device and the collar so that as the device is tightened the wrenching device breaks off at a pre-set torque. The break-off torque depends on the depth of the groove, which can be selected to meet different torque requirements.
The collar is a surface of revolution, so that once installed it cannot be rotated by conventional wrenches, so that the pre-selected torque cannot be later inadvertently changed. This "tamper proof" feature eliminates torque inspection after installation.
Such fasteners are widely available from the Hi-Shear Corporation under the "Hi-Lok" trademark and from several Hi-Shear licensees.
These fasteners are very effective and are intended to be permanently installed. Sometimes, however, the fasteners need to be removed due to assembly errors, need to repair the structure, etc. Where access is easy, a worker generally inserts an Allen wrench into the bolt end socket and rotates the collar with locking pliers. However, this technique damages the collar, and may damage the structure surface near the fasteners, especially if the pliers slip during unthreading. Also, tools must be held and operated simultaneously with both hands, requiring some skill and increasing the likelihood of errors and tool slips. Most importantly, access to a relatively large volume of space around the collar is required for these removal tools. Complex aerospace structure often have such fasteners in locations such that the collar is in a "well" or "tunnel" like areas, making access difficult. Special tools, such as the HLH128 Removal Tool from the Hi-Shear Corporation basically uses an offset cam-type closed end wrench to grip the collar while an Allen wrench engages the bolt socket. While this reduces the space needed for access, it still requires two-hand, skilled operation and could result in damage to adjacent surfaces if errors are made.
Other tools remove the collar by splitting it with a high pressure wedge device such as the collar splitters available from American Pneumatics Tool Co. and the Huck Co. While effective, these tools tend to be large, heavy and requires considerable access space and require hydraulic or high pressure air supplies. Other manually operated collar removal tools, such as those available from Continental Air Tools, Inc. operate only in interference fit condition and require considerable effort.
Thus, there is a continuing need for improved devices to operate in both interference and loose fit conditions which are lightweight, require little skill to use, require little access space around the fastener, reduce the risk of damage to adjacent structures, and save time.